The air pollutants exist in two major physical phases: the particle phase pollutants are pollutants with significant physical sizes including dust particles, airborne bacteria and mold, they may be composed and be bound together by different matters with different compositions, with sizes range from 1/100 micron to a few hundred micron; the gaseous phase pollutants are pollutants with simple chemical structures, the size of the gaseous phase pollutants are small from angstrom to nano-scale. Odor molecules and volatile organic compounds are examples of gaseous phase pollutants.
To deal with these two types of pollutants, different techniques of purification methods are generally employed. Filtration is one of the conventional purification methods. High efficiency particulate air filter (HEPA Filter) may be employed to remove the pollutants from the air. Other method such as generating high voltage by electrostatic precipitator or by emitting negative ions, which further charges up the suspended particulates and dust matters in the air, and collection the negatively charged suspended particulates and dust matters by the neutral or positively charged surfaces may also be employed. There also methods which employ the activated carbon, molecular sieves, zeolites as the filtering material, or with the further application of ozone, oxidants, UV light, complementary with the photo-catalyst or other different catalyst materials to oxidize and decompose the pollutants by catalytic oxidation decomposition. Different purification methods have their respective own characteristics and performances. They may be used to deal with different kinds of pollutants. Nonetheless, the conventional market available air purifiers often employ more than one type of the purification methods and technologies. Regardless on which purification methods being employed, the filters being used in these air purifiers are usually arranged one by one in a parallel manner. A fan is usually equipped inside the air purifiers, for drawing or blowing the air from the upstream to the downstream positions, and forcing the air to pass through all the filter layers.
Different filters have different physical and chemical properties. The methods of purification such as filtration, adsorption or electrostatic precipitation are characterized with different filter static pressures, some filters have high static pressures, while some have low static pressures, some even do not possesses any static pressure at all. Owing to the fact that different sources of pollutants can be found at different levels, the air purification becomes a complicated subject.
The conventional arrangement of filter which the filters are arranged in a parallel manner, by the application of a single blower to draw or to blow the air across the filters, letting the pollutants to be treated by these layers of filters under one single air flow rate, can hardly enable the filters be functionalized completely and cost-effectively. In some case, the life-span of the downstream filters may become shortened due to the in-effective filtration of pollutants by the upstream filters. In some worse case, the downstream filters may become deteriorate or they would become the pools for incubating and further emitting the pollutants, which in reverse, further worsen the environmental pollution.
U.S. Pat. No. 6,248,146 proposes a different method of filter arrangement. Therein, the filters were not assembled in a parallel manner. In order to make the air flow through the secondary air filters (124), a primary throat aperture (106) is designed, when the air flow through the primary throat aperture (106), its speed will be accelerated. The pressure inside the secondary air guide (112) would be reduced, the outside air is then drawn through the secondary air filter (124) into the secondary air guide (112), wherein they are being mixed with the original airflow in the static regain section (116), through the output filter (126) the air is discharged. This patent does not explicitly described whether an exhaust fan or blower will be used. Nevertheless, whatever an exhaust fans or a blower being employed, the practical application of it still embedded with some significant disadvantages. If an exhaust fan is being used to draw the air out from the device, the primary throat aperture (106) will induce a high-frequency noise. If a blower is being used to blow the air into the device, apart from having the disadvantage of high-frequency noise being produced as mentioned, the device would need to have a even much more narrower primary throat aperture (106) compare to the case when the exhaust fan is being used, in order to ensure the secondary air guide (112) having sufficiently negative pressure effect for letting the outside air go through the secondary air filter (124). Further more, if a blower is being used, the motor torque for the blower should be of extraordinary large value, in order to overcome the drag effect caused by the resistance induced by the narrow primary throat aperture (106). The situation is similar to the case when the air is to blown through the a drinking straw with one's mouth, if one slightly flattened the middle of the straw with his fingers, then he would required to input much more energy to blow the air through the drinking straw. More energy will be consumed with higher motor torque, which apart from leading to higher cost of operation, the noise level of the devices will further be increased.